1. Technical Field of the Invention
The present invention relates to a bump forming method of and bump forming apparatus for forming bumps on electrode portions, which are to be formed as so-called semiconductor device terminals, of a semiconductor wafer, a board having an electronic circuit formed thereon, or the like, using conductive particles.
2. Description of Prior Arts
There have been many kinds of bump forming methods and bump forming apparatuses. For example, there are a plating method in which metal is deposited on electrode portions of a semiconductor device through plating to form bumps, a printing method in which solder paste is printed on electrode portions of a semiconductor device and then heated to melt the solder in the solder paste to form bumps, and a stud bump method in which an end of a metallic wire is connected to an electrode portion of a semiconductor device and then the connected wire is cut off to form bumps.
Further, there is a solder ball mounting method in which solder balls (conductive particles) are sucked into a jig by vacuum suction to apply flux onto bottom surfaces of the solder balls, and the solder balls are mounted onto electrode portions of a wafer or a circuit board, and then the solder balls are heated and melted to form bumps.
As electronic products are being downsized and grown more powerful, the bump pitch and the bump diameter are rapidly being decreased as an IC package is changed from a QFP (quad flat package) to a BGA (ball grid array) and further from a CSP (chip size package) to a flip chip.
As the IC is being downsized, the conventional plating method is difficult to form bumps having a sufficient volume and further has a problem that the plating time requires a long time.
On the other hand, the conventional printing method has a problem that when the bumps of an IC are connected to a circuit board or the like, it is difficult to connect all of the bumps correctly because deviations occur in the bump volume and the bump height.
Further, the conventional stud bump method has a problem that the electrically conductive material of the circuit board used for being connected to the bumps is limited because the material of the bumps is gold.
Further, the conventional solder ball mounting method has the problems that number of balls capable of mounting at a time is only several hundreds and that the ball can not be mounted unless the diameter of the ball is above 300 xcexcm though the bumps can be formed without deviations in the bump volume and the bump height.
In addition to the above problems, there is a problem that since time required for mounting the solder ball is approximately 15 seconds/mounting, it takes more than several hours to mount several tens thousands solder balls and accordingly the productivity is low.
In more detail, there are the following technologies A to I known in the art which are described below. As disclosed in Japanese Patent Application Laid-Open No. 9-46704, a bump forming method of known technology (Example A) comprises a flux applying process of partially applying flux only surfaces of pads on a circuit board to form the bumps thereon; a solder ball adhering process of flux-adhering solder balls onto the surfaces of the solder pads through a mask having through holes capable of letting the solder balls pass through, the through hole being opposite to the solder pad; and a heating process of heating at a solder melting temperature after removing the mask to forming the solder bump.
In the bump forming method of Example A, many solder balls remaining in the regions other than the through holes of the mask are dropped down by turning over the circuit board and the mask together.
As disclosed in Patent Publication No. 2663927, a bump forming method of known technology (Example B) comprises a solder paste printing process of partially printing solder paste only onto surfaces of solder pads on a circuit board to form solder bumps thereon; and a solder ball pressing process of rutting solder balls into through holes of a mask opposite to the solder pads and capable of letting the solder balls pass through and pressing the solder balls from the upper side using projections each having a diameter smaller than the diameter of the solder ball.
As disclosed in Japanese Patent Application Laid-Open No. 6-291122, a bump forming method of known technology (Example C) is that perforations with bottom are bored in a mask, and solder balls are put into these perforations, and then excess solder balls are discharged through a solder ball discharging port by moving a brush along the upper surface of the mask.
As disclosed in Japanese Patent Application Laid-Open No. 7-254777, a bump forming method of known technology (Example D) is that a solder pad forming solder bumps on a chip part and a mask having through holes capable of letting solder balls pass through are positioned, and then the solder balls supplied to a box-shaped side wall are moved so as to be dropped into the through holes of the mask.
As disclosed in Japanese Patent Application Laid-Open No. 7-202403, a bump forming method of known technology (Example E) is that a solder pad forming solder bumps on a chip part and a mask having through holes capable of letting solder balls pass through are positioned, and then the solder balls supplied to a ball hopper are moved so as to be dropped into the through holes of the mask.
As disclosed in Japanese Patent Application Laid-Open No. 9-107045, a bump forming method of known technology (Example F) is that solder paste is partially applied onto only the 26 surfaces of solder pads on a BGA package to form solder bumps thereon, and a mask having through holes capable of letting solder balls pass through is positioned, and then a squeegee is moved to put the solder balls into the through holes of the mask.
As disclosed in Japanese Patent Application Laid-Open No. 11-135565, a bump forming method of known technology (Example G) is that flux is partially applied onto only the surfaces of bump pads on a board to forming solder bumps thereon, and a mask having through holes capable of letting solder balls pass through is positioned, and then the solder balls are heated after pressing the solder balls using a solder ball pushing plate.
As disclosed in Patent Publication No. 2713263, a bump forming method of known technology (Example H) is that cream solder is partially applied onto only the surfaces of pads on a print board to form solder bumps thereon, and a nozzle portion having a through hole capable of letting solder ball pass through is positioned, and then the solder ball is heated after pressing the solder ball in the nozzle portion onto the print board.
As disclosed in Patent Publication No. 2891085, a bump forming method of known technology (Example I) comprises a flux applying process of partially applying flux only surfaces of solder ball electrodes on a semiconductor element to form bumps thereon; a process of adhering solder balls onto the surfaces of the solder ball electrodes through a mask having through holes capable of letting the solder balls pass through, the through hole being opposite to the solder pad; and a process of dropping down many solder balls remaining in the regions other than the through holes of the mask by slightly tilting the semiconductor element and the mask together.
Further, there is a known technology titled xe2x80x9cSolder Ball Supply Apparatusxe2x80x9d disclosed in Japanese Patent Application Laid-Open No. 9-134923 which is similar to Example A.
In addition to the known technologies of Examples A to I, there is another known technology titled xe2x80x9cMethod of Mounting Conductive Balls on a Substratexe2x80x9d disclosed in Patent Application Laid-Open No. 2000-133923.
The xe2x80x9cmethod of mounting conductive balls on a substratexe2x80x9d disclosed in Patent Application Laid-Open No. 2000-133923 is that a flat-plate shaped positioning means having many conductive ball receiving holes is arranged on a downward tilt, and a plurality of conductive balls are supplied to the positioning means from a ball storing hopper to be put into the ball receiving holes.
The conductive balls not entered into the ball receiving holes are received into a conductive ball collecting hopper.
The positioning means receiving the many conductive balls is rotated so as to be in a horizontal position, and the conductive balls on the positioning means are attracted by a conductive ball attracting means.
After that, the conductive ball attracting means attracting the conductive balls is mounted on an electrically non-conductive member supply portion.
However, the conventional bump forming methods of (Example A) to (Example I) described above have problems as follows.
The first problem of the structure in the conventional bump forming methods is that the conductive particles adhere to each other.
This is a phenomenon that often occurs in particles having a diameter smaller than 300 xcexcm, and is caused by the van der Waals attraction due to charging of the conductive particles or unevenness of electron density of the conductive particles.
For example, when the conductive particles are dropped into the through holes of the mask while being slid the supply unit or on the mask using the brush, the squeegee or the like, static electricity is generated by contact between the conductive particles to each other and between the conductive particle and the mask, the supply unit, the brush, the squeegee or the like.
Since the conductive particles adhere onto the surface portion of the mask or the inside of the through holes of the mask, and the supply unit or the brush, the squeegee or the like by the static electricity, movement of the conductive particles can not be controlled, and accordingly the conductive particles can not be certainly supplied into the through holes of the mask by the self-weight.
Further, since the conductive particles adhere to halfway positions, in incomplete states, of the though holes of the mask due to the influence of the static electricity, there occurs a phenomenon that the conductive particles are seized in the tip end portion of the supply unit or the end surface portion of the squeegee to cause damage of the conductive particles.
The second problem of the structure in the conventional bump forming methods is that the conductive particles are apt to be deformed by external forces acting on the conductive particles because the conductive particles are slid on the mask using the squeegee or the brush, and accordingly the conductive particles can not be certainly inserted into or supplied to the though holes of the mask by the self-weight when the conductive particles are deformed by an amount above a diameter of the through holes of the mask.
The third problem of the structure in the conventional bump forming methods is that when the mask is removed from the wafer or the circuit board after putting the many conductive particles into the through holes of the mask, the conductive particles mounted on the electrode portions on the circuit board are apt to drop down due to friction between the inner surface of the though hole of the mask and the conductive particle.
Here, describing on the known technology of Example A described above, since the solder balls are dropped into the through holes of the mask only using the self-weight of the solder ball, there is a problem that the solder balls are charged and the many solder balls stay and remain at positions other than the through holes of the mask. However, the influence of the static electricity is not taken into consideration.
In addition to this, there is a problem in that the solder balls introduced into the through holes of the mask are apt to be dropped down by vibration of the mask produced when the circuit board and the mask are turned over. However, this influence of the vibration is not taken into consideration.
Further, the known technology of Example B does not take into consideration how to put the solder balls into the through holes of the mask. Furthermore, there is no consideration on the influence of the static electricity which is produced by the friction between the solder ball and the through hole of the mask when the solder balls are pushed out onto the upper portions of the circuit board by pushing out the positioned projections.
Further, since such a structure is taken that the solder balls put in the perforations of the mask are dropped to the convex solder pad forming the solder bump on the circuit board, the solder balls are dropped into the through holes of the mask by the self-weight due to charge of the solder balls when the mask and the circuit board are turned over.
Further, the conductive particles are apt to be deformed by external forces acting on the conductive particles because the structure is that the solder balls of the conductive particles are slid on the mask using the brush, and accordingly the conductive particles can not drop into the through holes of the mask by the self-weight when the conductive particles are deformed by an amount above a diameter of the through holes of the mask.
The structure of the known technology of Example D is that since the mask and the surfaces of the solder balls and the box-shaped inner wall are charged by movement of the solder balls supplied to a box-shaped side wall, the solder balls put in the through holes are apt to spring out from the perforations of the mask.
Further, since the solder balls adhere to halfway positions of the though holes of the mask, there occurs the phenomenon that the solder balls are apt to be chipped by being seized in the corner portion of the box-shaped storing frame.
Further, the conductive particles are apt to be deformed by external forces acting on the conductive particles because the structure is that the conductive particles are slid on the mask using the box-shaped storing frame, and accordingly the conductive particles are difficult to be dropped into the through holes of the mask by the self-weight when the conductive particles are deformed by an amount above a diameter of the through holes of the mask.
Further, the structure of the known technology of Example E is that since the mask and the surfaces of the solder balls and the inner wall of the ball hopper are easily charged by moving of the solder balls supplied to the box-shaped ball hopper, the solder balls put in the through holes of the mask are apt to spring out from the perforations of the mask.
Further, since the solder balls adhere to halfway positions of the through holes of the mask by the static electricity, there occurs the phenomenon that the solder balls are apt to be chipped by being seized in the end portion of the ball hopper or the pressing member.
Further, the conductive particles of the conductive particles are apt to be deformed by external forces acting on the solder balls because the structure is that the conductive particles are slid on the mask using the ball hopper, and accordingly the conductive particles are difficult to be dropped into the through holes of the mask by the self-weight when the conductive particles are deformed by an amount above a diameter of the through holes of the mask.
Further, the structure of the known technology of Example F is that since the mask and the surfaces of the solder balls and the squeegee are easily charged by moving of the solder balls supplied to the sword-tip-shaped squeegee, the solder balls once put in the through holes of the mask are apt to spring out from the perforations of the mask.
Further, since the solder balls adhere to halfway positions of the through holes of the mask by the static electricity, there occurs the phenomenon that the solder balls are apt to be chipped by being caught by the squeegee.
Further, the conductive particles are apt to be deformed by external forces acting on the conductive particles because the structure is that the conductive particles are slid on the mask using the sword-tip-shaped squeegee, and accordingly the conductive particles are difficult to be dropped into the through holes of the mask by the self-weight when the conductive particles are deformed by an amount above a diameter of the through holes of the mask.
The known technology of Example G does not consider how to put the solder balls into the through holes of the mask.
Further, the structure of the known technology of Example H is that the metallic balls are apt to be caught by the corner of the through holes of the nozzle portions when the pressing portions are inserted into the through holes of the pressing portions. Further, the structure is that the metallic balls are apt to be deformed by external forces acting on the metallic balls.
Further, the structure of the known technology of Example I is that since the solder balls are put into the through holes of the mask while the solder balls are being slid from the upper portion of the mask to the down portion in a state that the semiconductor element and the mask are slightly tilted, the solder balls are charged by friction between the solder balls and the mask and accordingly the solder balls are apt to remain on the mask.
Further, the structure is that the solder balls once entering the through holes are apt to spring out due to the charge of the balls.
For example, in a case where the conductive particle is made of a solder having tin, lead or silver as the main component, and the diameter is smaller than 300 xcexcm, static electricity of xc2x150 to xc2x13000 V is generated between the mask and the solder balls when the solder balls are slid on the mask.
The conventional technologies described above have not been practically used because the structure is that the conductive particles are difficult to be dropped into the through holes of the mask due to the influence of the static electricity and the van der Waar force produced on the surfaces of the conductive particles, and because the problem of producing the damage such as forming chips in the conductive particles can not solved due to the structure that the conductive particles are apt to be caught by the tip end portion of the supply unit such as the hopper or the like.
An object of the present invention is to provide an economical bump forming method and an economical bump forming apparatus by which bumps can be formed on electrode portions of a wafer or a circuit board (or substrate) using spherical conductive particles having a given dimensional accuracy in order to make the deviations of bump height and volume of conductive particles having a diameter smaller than 300 xcexcm.
Further, another object of the present invention is to provide a bump forming method and a bump forming apparatus recyclable of the conductive particles by certainly and easily sucking and collecting the excess conductive particles remaining on the mask to reuse the expensive conductive articles.
In order to attain the above objects, the present invention is constructed as follows.
(1) A bump forming method which forms bumps on electrode portions of a semiconductor wafer or an electronic circuit board using conductive particles, the method comprising a process of positioning a mask having through holes for the conductive particles at bump forming positions to the wafer or the circuit board, and putting the mask and the wafer or the circuit board on a table having suction holes formed thereon; a particle mounting process of moving a conductive particle supply means while the conductive particles are being dropped on the mask, and sucking the conductive particles through the holes formed on the table via the through holes formed in the mask in synchronism with a moving position of the conductive particle supply means, and mounting the conductive particles onto the electrode portions of the semiconductor wafer or the electronic circuit board; and a ball collecting process of collecting the conductive particles not dropped into the through holes of the mask.
(2) In the bump forming method according to the above item (1), it is preferable that a groove for sucking the conductive particles is formed in a tip end portion of the conductive particle supply means, and the conductive particle supply means controls holding and dropping of the conductive particle by controlling sucking and not-sucking of the conductive particle using the sucking groove.
(3) In the bump forming method according to any one of the above item (1) and the above item (2), it is preferable that a charge neutralizing fluid is blown to the conductive particles contained in the supply means.
(4) In the bump forming method according to any one of the above items (1), (2) and (3), it is preferable that a vibrator is arranged on a side surface of a conductive particle containing portion of the supply means, and the conductive particles are dropped down from the supply means while vibration is being added to the conductive particles.
(5) In the bump forming method according to any one of the above items (1), (2), (3) and (4), it is preferable that flux or solder paste or conductive adhesive is attached onto the electrode portions on the semiconductor wafer or the circuit board in advance, and then heat is supplied from an upper side of the thorough holes of the mask after dropping the conductive particles to increase a sticking force between the electrode portion and the conductive particle.
(6) In the bump forming method according to any one of the above items (1), (2), (3), (4) and (5), it is preferable that the conductive particles not dropped into the through holes of the mask are collected by a particle collecting means, the particle collecting means comprises an suction portion for sucking the conductive particles, and many slit grooves are formed in an inlet port of the suction portion to collect the conductive particles by producing a turbulent flow in the suction portion.
(7) In the bump forming method according to any one of the above items (1), (2), (3), (4), (5) and (6), it is preferable that a surface material of the table has a film made of any material of iron, zirconia, alumina or zirconia or chromium, and titanium.
(8) In the bump forming method according to the above item (5), it is preferable that a material boiling temperature of the flux, the solder paste or the conductive adhesive is higher than a melting point of the conductive particle by +10xc2x0 C. to +40xc2x0 C.
(9) In the bump forming method according to any one of the above items (1), (2), (3), (4), (5), (6), (7) and (8), it is p referable that the conductive particles are collected, subjecting the collected conductive particles to separation of the conductive particles and dust using a centrifuge in a centrifugal chamber.
(10) A bump forming apparatus for forming bumps on electrode portions of a semiconductor wafer or an electronic circuit board using conductive particles, which comprises a mask having through holes for the conductive particles at positions to form the bumps thereon; a table having a plurality of suction holes, the wafer or the circuit board being placed on the table, the conductive particles being sucked through the suction holes via the through holes formed in the mask; a conductive particle supply means moving while dropping the plurality of conductive particles into the through holes of the mask; and a conductive particle collecting means for collecting the conductive particles, wherein the conductive particles are sucked through the holes formed in the table via the through holes formed in the mask in synchronism with positions to be mounted onto electrode portions on the semiconductor wafer or the electronic circuit board, and the conductive particles not dropped into the through holes of the mask are collected by the conductive particle collecting means.
(11) In the bump forming apparatus according to the above item (10), it is preferable that a groove for sucking the conductive particles is formed in a tip end portion of the conductive particle supply means, and the conductive particle supply means controls holding and dropping of the conductive particle by controlling sucking and not-sucking of the conductive particle using the sucking groove.
(12) In the bump forming apparatus according to any one of the above item (10) and the above item (11), it is preferable that a charge neutralizing fluid is blown to the conductive particles contained in the supply means.
(13) In the bump forming apparatus according to any one of the above items (10), (11) and (12), it is preferable that a vibrator is arranged on a side surface of a conductive particle containing portion of the supply means, and the conductive particles are dropped down from the supply means while vibration is being added to the conductive particles.
(14) In the bump forming apparatus according to any one of the above items (10), (11), (12) and (13), it is preferable that flux or solder paste or conductive adhesive is attached onto the electrode portions on the semiconductor wafer or the circuit board in advance, and then heat is supplied from an upper side of the thorough holes of the mask after dropping the conductive particles to increase a sticking force between the electrode portion and the conductive particle.
(15) In the bump forming apparatus according to any one of the above items (10), (11), (12), (13) and (14), it is preferable that the conductive particles not dropped into the through holes of the mask are collected by a particle collecting means, the particle collecting means comprises an suction portion for sucking the conductive particles, and many slit grooves are formed in an inlet port of the suction portion to collect the conductive particles by producing a turbulent flow in the suction portion.
(16) In the bump forming apparatus according to any one of the above items (10), (11), (12), (13), (14) and (15), it is preferable that a surface material of the table has a film made of any material of iron, zirconia, alumina or zirconia or chromium, and titanium.
(17) In the bump forming apparatus according to the above item (14), it is preferable that a material boiling temperature of the flux, the solder paste or the conductive adhesive is higher than a melting point of the conductive particle by +10xc2x0 C. to +40xc2x0 C.
(18) In the bump forming apparatus according to any one of the above items (10), (11), (12), (13), (14), (15), (16) and (17), it is preferable that the conductive particles are collected subjecting the collected conductive particles to separation of the conductive particles and dust using a centrifuge in a centrifugal chamber.